Process of making extruded powder



Patented Aug. 7, 1945 PROCESS OF MAKING EXTRUDED POWDER Charles Earnest Silk, Alton, 111., asslgnor to Olin Industries, Inc., a corporation of Delaware No Drawing.

Claims.

This invention relates to explosives, in particular to smokeless powder, and provides an improved process of manufacturing extruded grains thereof,

Powder grains have heretofore been manufactured by a procedure in which the powder base was gelatinized with ether-alcohol mixtures, ethyl acetate-alcohol mixtures, or acetone and the like, the gelatinized base then being extruded into the desired form of grain and the solvent being removed from the grain by an air-drying treatment or by an air-drying treatment followed by a gradual extraction with water or, in some instances, by a gradual extraction with water followed by an air-drying treatment. Such solventremoving treatments, employed in generalpractice on powder grains containing the usual watermiscible solvents, were very time consuming. For instance, several weeks were required for the removal of solvent from powder grains of the size used in 75 mm. field pieces.

An object of this invention is to provide an improved process for the manufacture of extruded grains of smokeless powder.

Another object of the invention is to provide a process for the manufacture of extruded grains of smokeless powder wherein a novel gelatinizing composition is employed and a much shorter time is required for removing the solvent fromv the grains than heretofore.

A further object of the invention is to provide a process whereby the removal of solvent from the gelatinized powder base is facilitated.

Still further objects and advantages will be apparent from the following description.

In accordance with this invention the foregoing objects may be accomplished by gelatinizing the powder base with a solvent mixture containing a solvent and a non-solvent for the powderbase, both of which are volatile and water-immiscible or only very slightly water-soluble, extruding the gelatinlzed material into grains, immersing the grains in an aqueous bath, in which the solvent mixture is substantially insoluble, and thereafter rapidly removing the volatile solvent constituents from the grain by distillation.

In accordance with this procedure, therefore, advantage is taken of the fact that, with the use of a gelatinizing composition which is substantially insoluble in the aqueous distillation bath, the volatile constituents may be rapidly removed from the powder grain by distillation without changing the uniformly gelatinized condition of the grain. The total time for preparing such solvent-free grains is thereby considerably shortened.

Application January 6, 1941, Serial No. 373,312

This advantage was not obtainable in the processes heretofore in use since such treatment caused water to enter the powder grains containing the water-miscible solvents and resulted in a precipitation of the powder base, the resultant grains being entirely unsatisfactory both from the standpoint of mechanical resistance and ballistics. Accordingly, it was necessary to remove the solvents very slowly from the powder base either by air-drying or by'both air-drying and water extraction.

Although removal of the solvent from the grains can be effected by a procedure involving rapid distillation, when a water-immiscible solvent such as ethyl acetate is employed alone as the gelatinizing agent, a dimcult-handling problem is presented due to the tackiness of the mixture obtained. Likewise, high extrusion pressures are required and an undue amount of shrinkage of the grain occurs leading to non-uniform and, at times, distorted grains.

By including a water-immiscible organic liquid non-solvent in the composition, in accordance with this invention, tackiness of the mixture is avoided, thus rendering the solvent-wet gelatinized material easier to handle, lower extrusion pressures may be employed, and the shrinkage of the grain when the solvent is removed therefrom is greatly minimized.

The process of thi invention may be applied in the manufacture of extruded smokeless powder grains of any suitable powder base. The base, for example, may consist of nitrocellulose of any desired degree of nitration, viscosity, or physical form, or a mixture of different types of nitrocellulose. The nitrocellulose may be replaced wholly or in part by other high molecular weight smokeless powder bases such as nitrostarch, capable of being dispersed in a volatile solvent and of being converted to a coherent gelatinized solid upon evaporation of the solvent. The smokeless powder base may also contain other active explosive ingredients such as nitro-aromatic compounds, for example, diand tri-nitrotoluene or nitric acid esters of polyhydroxy compounds such as nitrogLvcerine, nitroglycol, nitromannite, and pentaerythritol tetranitrate or other explosive organic nitrates or nitro compounds, for example nitramines such as nitro-guanidine. Other agents may be included for securing desired characteristics such as, for example, stabilizers, deterrents, water-proofing agents and other substances adapted to produce specific effects.

When nitrocellulose is utilized as the smoke state preferably after having been stabilized by suitablei treatment. The starting material may likewise consist of previously gelatinized nitrocellulose. For example, it may be in the form of small globules or particles with or without residual solvent, or in finely divided form, which may be obtained, for instance, by grinding and stabilizing deteriorated cannon powder grains. Similarly, the raw material may consist of gelatinized nitrocellulose-nitroglycerine powders.

Where the powder base to be employed is in an oven-dry or substantially air-dry condition, the gelatinizing composition may be added directly thereto with suitable mixing to uniformly gelatinize the powder base. Ordinarily, however, powder bases, such as fibrous nitrocellulose or gelatinized nitrocellulose mixtures, are received in a water-wet condition directly from the stabilizing treatment. Before such powder bases can be suitably gelatinized and extruded, it has been found preferable to remove the water content, for instance, by dehydration.

Alcohol has ordinarily been employed to dehydrate nitrocellulose, but since alcohol is watermiscible, it is not suitable as the sole non-solvent component of the gelatinizing composition, in the present process. Therefore, it is preferable to displace the alcohol in the powder base with a non-solvent suitable as the non-solvent component of the gelatinizing composition. This dehydration may be readily accomplished in the usual dehydrating apparatus by first displacing the water in the powder base with alcohol and thereafter displacing the alcohol in the powder base with the non-solvent to be employed. Any other suitable means of dehydration may likewise be employed, for instance, the alcohol displacement may be omitted and the water may be removed by distillation in the presence of an excess of the water-immiscible non-solvent to be employed in the gelatinizing mixture.

The non-solvent employed in the gelatinizing mixture may consist of one or more volatile diluents, such as aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, ethers, and the like, for instance, benzene, toluene, xylene, pentane, ethylene chloride, chlorobenzene and isopropyl ether.

After dehydration of the powder base, it is gelatinized by incorporating the necessary amount of solvent in suitable kneading or mixing apparatus. The solvent used to gelatinize the powder base is one which is substantially immiscible with the aqueous bath referred to hereinafter and which is sufllciently volatile to be removed from the powder grains by evaporation. Generally, both the solvent and the non-solvent of the gelatinizing composition should have a boiling point below or not greatly in excess of 100 0., although liquids of somewhat higher boiling points may, at times, be suitable. For instance, suitable organic liquid solvents are aliphatic esters, such as ethyl acetate, isopropyl acetate, butyl acetate, and ethyl formate, and aliphatic ketones, such as methyl ethyl ketone or methyl isobutyl ketone.

The amount of solvent and non-solvent in the gelatinizing composition most suitable for use in any given instance will depend largely on the characteristics, such as solubility and viscosity of thefparticular smokeless powder base and the extrusion pressures employed. It is preferred to employ an amount of non-solvent only slightly less than that required to precipitate the powder base fromfthje, solvent during removal of the gelatinizing composition, although lesser amounts may be employed to good advanta e, for instance, with some non-solvents as low as 10% to 20% of the solvent mixture. For example, gelatinizing compositions containing from 50% to 65% benzene and from 50% to 35% ethyl acetate have been found entirely satisfactory for cellulose nitrate soluble therein.

It is usually preferable to employ only just sufficient solvent mixture to uniformly gelatinize the powder base and form a workable mass which can be extruded satisfactorily in the extrusion equipment available. For instance, the amount of solvent mixture employed will usually be in the range of from 85% to 105% of the weight of powder base used, depending for the most part on the solubility and viscosity of the powder base in the composition. When the powder base, dissolved in the water-immiscible solvent mixture, forms a very viscous; diflicultly workable dough. it is sometimes advisable to use more than one type of non-solvent. For instance. when employing a solvent mixture composed of ethyl acetate and benzol, the viscosity of they dough may in some instances be greatly reduced by adding a small amount, usually not more than about 10%, of an oxygen-containing nonsolvent such as ethanol or methanol to the mixture.

Other desired ingredients may be incorporated during the mixing operation, for instance, there may be added the desired amount of'stabilizer, such as diphenylamine or a dialkyldiphenylm'ea such as methyl or ethyl centralite or mixtures thereof, deterrents such as dinitrotoluene, dibutylphthalate, diamylphthalate, or diphenylphthalate, accelerators such as nitroglycerine, or water-proofing agents. After thorough mixing, the material may be treated in the usual blocking and macaroni presses to increase its homogeneity.

After the material has been uniformly mixed, it is extruded into grains of the desired size and shape. It is to be understood that the process f forming grains described herein as extruding includes all molding processes such as forcing the gelatinized material through suitable dies and cutting it into grains, passing the gelatinized material through rolls to form sheets which may then be further subdivided to any desired extent to form strips or flakes, pressure molding and the like.

The grains thus formed are placed in an aqueous bath and the solvent is then distilled therefrom by raising the temperature of the bath.

The aqueous bath employed for distilling the major portion of solvent from the powder grains is not a solvent for the smokeless powder base and preferably consists of a concentrated solution of a salt, such as from 15% to a saturated solution of sodium sulfate. It will be understood. however, that salts other than sodium sulfate, for instance sodium chloride, potassium chloride, or potassium nitrate may at times be useful. The presence of the salt in the distillation bath tends to further reduce the solubility. of the gelatinizing composition in the bath and thus aids in preventing the precipitation of the powder base. Further, it is to be understood that aqueous bath" and water," as used herein to describe the distillation bath, are to be construed as including other suitable media which are not solvents for the powder base and in which the gelatinizlng composition is substantially immiscible.

During the distillation, the slurry of powder grains is agitated to prevent the grains from sticking together and to aid in the removal of the solvent composition. Air may be bubbled up through the slurry to aid in the solvent removal, especially during the latter stages of the distillation. Likewise, the presence of a small amount of protective colloid, such as gum arabic, starch, or animal protein in the aqueous bath tends to prevent adhesion of the grains.

After removal of the major portion of the gelatinizing composition, the removal of the final traces may be facilitated by reducing the salt concentration of the aqueous distillation bath, or by finally treating'the grains in water alone. This operation of removing the solvent from the grains requires only a relatively short time as compared with prior processes, wherein watermiscible solvents were used, and the hazard connected therewith is considerably less.

In order to illustrate the process of this invention, a detailed description is given below of one embodiment employing fibrous nitrocellulose as the starting material for manufacturing propellent powder grains of a size suitable for use in '75 mm. fields pieces, the grains having a web thickness of about ;025 inch, a length of about 0.355 inch, a diameter of about 0.142 inch, and provided with seven longitudinal perforations.

Twenty parts by weight of fibrous cellulose nitrate consisting of about 40% pyro-cotton having about 12.6% nitrogen and 60% gun cotton having about 13.45% nitrogen, water-wet from the stabilizing treatment, is placed in the usual type dehydration press, blocked and subjected to the usual water displacement wash with alcohol. After the water is displaced with alcohol a major portion of the alcohol is then displaced with benzol so that the liquid content of the nitrocellulose mixture consists of at least about 90% benzene.

Then benzol-wet cellulose nitrate is then pressed into a cake of about 30.44 parts by weight. The cake is then broken in a suitable defibering machine and transferred to a Wemer-Pfleiderer mixer. About 6.96 parts by weight of ethyl acetate, 1.13 parts by weight of methyl centralite and 1.13 parts by weight of dibutyl phthalate are then added to and incorporated in the nitroceL lulose in the mixer. After thorough mixing the material is then placed in a blocking press, blocked at a pressure of about 3000 to 4000 pounds per square inch, macaronied, re-blocked, and flnally extruded at about1700 to 3000 pounds per square inch pressure through a die of proper size and in the usual equipment employed for the preparation of this type of product.

After the grains have been out, they are placed in a water solution containing about 20% sodium sulphate and /z% gum arabic at a temperature of about 30 C.-40 C. The slurry, consisting of about 2-8 parts of salt solution to 1 part of powder, is continuously agitated while the solvent is distilled from the grain. This operation may be carried out in any suitable equipment, for instance, a still provided with a vapor outlet and a condenser for the .purpose of recovering the solvent, suitable means for agitating the slurry and a jacket forheating the contents of the still.

The distillation schedule will vary for diii'erent sized powder grains but for powder grains of the 75 mm. size prepared above, the following distillation schedule has proven satisfactory. The

salt solution is then drained from the grains and replaced by a fresh salt solution containing 10% sodium sulphate and the grains again treated for 8 hours at about C. to 97 C. This salt solution is then likewise drained from the grains and replaced by a fresh solution containing about 5% sodium sulphate and the grains are treated in the 5% solution for 8 hours at a temperature of about 95 C. to 07 C. This salt solution is then drained from the grains and the grains are washed free of sodium sulphate with warm water. Instead of adding fresh salt solution as described above, if desired, the original salt water.

bath may be diluted to the concentrations of sodium sulphate of 15%, 10% and 5% respectively,

although in some instances such a procedure may require a somewhat longer period of distillation in order to remove the solvent mixture.

At the end of such distillation treatment the grains are substantially free of solvent mixture and are ballisticaily stable. Where more than a trace of solvent still remains after such treatment it may be readily removed by further treatment with salt solution or with water alone. Thus, a period of only about 42 hours is required to remove the solvent from the powder grains, whereas with prior processes several weeks were required for this size of powder grain.

After the above described distillation, the powder is air-dried at a temperature of about 55 C. Powder grains prepared and treated as described above were found to have a total moisture and volatile content, after 16 hours air-drying at 55 C.. of only about 1.1%. The total time for the removal of solvent and drying of the powder was therefore only 58 hours.

Instead of carrying on the above described distillation at atmospheric pressures or higher, it may in some instances, be found desirable to em-' ploy a vacuum distillation in order to out down both the time and temperature of distillation. Vacuum distillation is especially desirable when a double base powder is to be prepared including the organic liquid solvent and non-solvent used.

For instance, in the manufacture of .30 caliber powder, a shorter period of distillation may be employed for a complete removal of the volatile solvent constituents than with 75 mm. powder and likewise with higher boiling solvents and nonsolvents higher distillation temperatures may be employed. Further, with low boiling solvents, too rapid a rise in temperature during distillation may result in a cracked or deformed grain due to too rapid an evolution of the solvent content so that with such solvents the temperature should be raised veryslowly.

The operating details hereinbefore described are, therefore, to be considered as illustrative of the invention and as many variations may be made withinits spirit and scope it should be understood that the present invention is limited only as set forth in the claims.

Having now described the invention, what claimed as new and is desired to be secured by Letters Patent is:

1. In the art of makingexplosives, the process which comprises replacing the water in a waterwet powder base with an alcohol, replacing the alcohol in said powder base with benzene so that the liquid content of the mixture consists of at least about 90% benzene, gelatinizing said powder base by incorporating in the mixture a volatile substantially water-immiscible solvent therefor, extruding the gelatinized powder base into grains, and thereafter removing the volatile constituents from said grains by distillation inan aqueous salt solution.

2. In ,the art of making explosives, the process which comprises treating a powder base with an amount of a substantially water-immiscible solvent composition sufllcient to uniformly gelatinize the powder base, said'solvent composition including a volatile substantially water-immiscible liquid solvent for said powder base and an amount of a volatile substantially water-immiscibl liquid non-solvent for said powder base sufiicient to reduce the tackiness of the mixture without precipitating the powder base, said non-solvent being selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons and ethers, and thereafter extruding the gelatinized powder base into grains.

3. In the art of making explosives, the process which comprises treating a powder base with an amount of substantially water-immiscible solvent composition sufficient to uniformly gelatinize the powder base, said solvent composition including a volatile substantially water-humiscible liquid solvent for said powder base and an amount of a volatile substantially water-immiscible liquid non-solvent for said powder base sufficient to reduce the tackiness of the mixture without precipitating the powder base, said non-solvent being selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, and ethers, extruding the gelatinized powder base into grains, and thereafter removing the volatile constituents from said grains by distillation in an aqueous bath.

4. In the art of making explosives, the process which comprises treating a powder base with an amount of a substantially water-immiscible solvent composition sufllcient to uniformly gelatinize the powder base, said solvent composition including a volatile substantially water-immiscible liquid solvent for said powder base and an amount of a volatile substantially water-immiscible liquid non-solvent for said powder base sufflcient to reduce the tackiness of the mixture without precipitating the powder base, said non solvent being selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, and ethers, extruding the gelatinized powder base into grains and thereafter removing the volatile constituents of the solvent composition from said grains by distillation in an aqueous salt solution.

5. In the art of making explosives, the process which comprises treating a powder base with an amount of a substantially water-immiscible solvent composition suflicient to uniformly gelatinize the powder base, said solvent composition including a volatile substantially water-immiscible liquid solvent for said powder base and an Lafamount of a volatile substantially water-immlscible liquid non-solvent for said powder base suiflcient to reduce the tackiness of the mixture without precipitating the powder base, said nonsolvent being selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, and ethers exstantially water-immiscible solvent therefor, said solvent being present in amount sufficient to uniformly gelatinize said powder base and said nonsolvent being present in amount sufficient to reduce the tackiness of the mixture without precipitating the powder base, extruding the gelatinized powder base into grains, and thereafter removing ,the volatile constituents from said grains by distillation in an aqueous bath.

7. In the art of making explosives, the process which comprises gelatinizing a powder base with a volatile liquid solvent composition including an amount of a substantially water-immiscible liquid solvent sufllcient to uniformly gelatinize the powder base, a substantially water-immiscible nonsolvent selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons, and ethers and present in an amount sumcient to reduce the tackiness of the mixture without precipitating the powder base, and an amount of a lower alcohol equal to not more than about 10% butsufllcient to reduce the viscosity of the gelatinized powder base, and thereafter extruding the gelatinized powder base into grains.

8. In the art of making explosives, the process which comprises replacing the water in a waterwet powder base with a volatile water-miscible organic liquid non-solvent for said powder base, replacing substantially all of the said volatile substantially water-miscible non-solvent in said powder base with a volatile substantially waterimmiscible liquid non-solvent selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons. and ethers, gelatinizing said non-solvent-wet powder base by mixing therewith a substantially water-immiscible liquid solvent therefor, said solvent being present in amount suillcient to .uniformly gelatinize said powder base and said nonsolvent being present in amount sufllcient to reduce the tacki'ness of the mixture without precipitating the powder base, extruding the gelatinized powder base into grains and thereafter removing the volatile constituents from said grains by distillation in an aqueous bath.

9. In the art of making explosives, the process which comprises replacing the water in a waterwet powder base with a lower alcohol, replacing at least about 90% of the alcohol in said powder gelatinizinz said non-solvent-wet powder base by mixing therewith a substantially water-immisfrom said grains by distillation in an aqueous salt solution.

10. In the art of making explosives, in which a powder base is gelatinized with a volatile liquid substantially water-immiscible solvent therefor and the gelatiniz ed mixture is extruded into V grains, the steps which comprise including in the gelatinizina mixture a volatile substantially water-immiscible liquid non-solvent selected from the group consisting of aromatic hydrocarbong, aliphatic hydrocarbons, chlorinated hydrocarbons, and ethers, in an amount sumcient to reduce the tackiness of the gelatinized mixture without precipitating the powder base therefrom. and removing the volatile constituents from the powder grains by distillation in an aqueous salt CHARLES EARNEST SILK.

10 solution. 

